Surgical Treatment of Isthmic Spondylolisthesis

Spondylolisthesis is defined as a forward slippage of the vertebral body together with its pedicles, transverse processes, and upper articular processes caused by a break in the continuity or an elongation of the pars interarticularis. Most commonly seen in the lumbosacral area, spondylolisthesis is caused by a variety of spinal pathologies, with the primary defect being a loss or compromise of the structural restraints that prevent the forward slipping of the spine. These key structural restraints include the articular facets, posterior arches, pedicles, and intervertebral disks.

Spondylolisthesis can result in several clinical entities based on the severity of the pathology. Many cases of spondylolisthesis are initially asymptomatic; however, symptoms may develop over time when combined with the degenerative changes that occur with aging. The most common presenting symptom with spondylolisthesis is isolated back pain. Neurologic symptoms may occur from central stenosis as a result of the subluxation or radicular symptoms from foraminal compression caused by facet hypertrophy or nerve root tension while the root is draped around the pedicles ( ▶ Fig. 45.1). Central or radicular symptoms can manifest individually or in combination. Children and young adults who participate in hyperextension-type activities or overhead sports, including gymnastics, football, and weightlifting, may have a predisposition to spondylolisthesis. In particular, these activities are specifically associated with spondylolysis that is a fracture or discontinuity of the pars interarticularis at the involved listhetic segment. In adults, spondylolisthesis may manifest with symptoms of tight hamstrings, pain in the back aggravated by flexion or extension, variable limited walking distance, or occasionally neurologic deficits.

Fig. 45.1 The pathognomonic feature of isthmic spondylolisthesis, defects in the pars interarticularis bilaterally.

The Wiltse-Newman classification divides spondylolisthesis into dysplastic, isthmic, degenerative, traumatic, and pathological. The isthmic spondylolisthesis group is further subdivided into spondylolytic, pars elongations secondary to healed microfractures, and acute pars fracture. Sponylolisthesis is graded from 1 to 5 according to the Meyerding classification system ( ▶ Fig. 45.2 a). Most authors agree that grade 3 and 4 slips are considered high-grade and are generally associated with higher incidence of progression and disabling symptoms. In addition to the translational deformity, high-grade slips can have angular deformity. ¹ The degree of angulation can be expressed as the slip angle ( ▶ Fig. 45.2 b). This slip angle or lumbosacral kyphosis can have a profound impact on the entire lumbar spine because the patient often compensates with hyperlordosis, which leads to facet joint changes, stenosis, and potential retrolisthesis proximal to the more obvious deformity, which is most commonly seen at the L5–S1 level. ²^, ³^, ⁴

Fig. 45.2 (a) The percentage of slippage is calculated by measuring the distance between the posterior borders for the cephalad vertebral body and the caudad vertebral body and then dividing that distance by the length on the inferior end plate. Grades 1 and 2 are considered low grade. Grades 3 and 4 are considered high grade. (b) The degree of angulation can be expressed as the slip angle, or lumbosacral kyphosis; this can be measured by drawing a line from the superior end plates of L5 and S1 and determining the angle made by these lines.

45.2 Patient Selection

The initial evaluation should begin with a detailed history and physical examination. ⁴ Adult patients often will not have a known activity-related injury but will more frequently describe a combination of axial back pain, neurogenic claudication, radiculopathy, or a combination of these. The axial back pain is typically mechanical, that is, positional and activity related. Pain generators include the pars defect and degenerated disks and facets. Neurogenic claudication symptoms are seen in patients with central stenosis, and these include bilateral buttock and thigh pain or discomfort that improves with flexion or rest. Patients with isthmic spondylolisthesis often commonly suffer from radicular symptoms related to foraminal stenosis. As the vertebral column slips anteriorly, the posterior arch will also slide anteriorly and decrease the ventral–dorsal dimensions of the canal and foramen, leading to spinal stenosis. Nerve root compression as a result of spinal stenosis in degenerative spondylolisthesis typically involves the traversing nerve root at the lateral recess resulting from facet hypertrophy of the superior articular facet compressing the nerve root over the listhesed disk.

Radiographic evaluation includes anteroposterior and lateral standing as well as standing flexion–extension radiographs. Oblique X-rays provide an orthogonal view of the pars, and the fracture may be seen as the collar on the scotty dog in this imaging view. Radiographs should be taken in the upright position as the slip may reduce in the supine position. Full-length standing films allow for calculation of both regional and global sagittal alignment as well as pelvic parameters. Additionally, computed tomography (CT) scans can be helpful in showing a pars interarticularis fracture. Axial images with sagittal and coronal reconstructions should be carefully scrutinized to identify these defects. Magnetic resonance imaging (MRI) scans can be used to detect neural compression, synovial cysts, and facet joint effusions and can give an assessment of the degree of intervertebral disk degeneration ( ▶ Fig. 45.3). Radiographic predictors of instability include spondylolisthesis, facet widening, end plate degenerative changes, sagittal facet orientation, and facet sclerosis. ¹

Fig. 45.3 Sagittal T2-weighted magnetic resonance imaging study of a 42-year-old man with a low-grade isthmic spondylolisthesis. Note the significant degenerative changes in the L5–S1 intervertebral disk and the relative enlargement of the spinal canal at this level.

No clear consensus has been reached on the optimal treatment paradigms for nonoperative versus operative interventions for spondylolisthesis. Conservative measures consist of activity modification, physical therapy, pain medication, anti-inflammatory drugs, muscle-relaxing drugs, bracing for acute injuries, or pain interventional procedures. Core strengthening and physical therapy, particularly including stretching of the hamstrings, may likewise minimize symptoms. Absolute indications for surgery include the presence of a neurologic deficit, a progressive slip or a slip of greater that 50%, high-grade slips in children, and severe lumbosacral deformity ¹ ( ▶ Fig. 45.4). Persistent back pain, with or without radicular symptoms, that does not respond to attempts at conservative treatment, as well as postural or gait problems and cosmetic concerns, are a relative indications for surgical intervention. Surgical intervention in adults focuses on decompression, whereas the emphasis in children is realignment.

Fig. 45.4 Lateral plain film radiograph of a 48-year-old woman with a high-grade slip at the L5–S1 level. This grade 3 anterolisthesis was associated with a collapsed L5–S1 disk in this active long-distance marathon runner.

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